The present invention relates generally to tools and methods used to compress a spring. More particularly, the invention relates to compressor tools and methods used to compress springs such as MacPherson type strut springs. Even more particularly, the invention relates to tools and methods utilizing a clam shell style strut spring compressor.
Coil springs are in wide use in vehicle suspension, such as car and truck suspensions. One type of coil suspension uses a MacPherson strut assembly which is a self-contained cartridge that has a coil spring surrounding a shock absorber.
Many types of tools and methods have been in use to compress a MacPherson strut spring. Compressing a MacPherson strut spring is needed for installation and removal of the strut and spring assembly. Accordingly, since many vehicles utilize MacPherson strut type suspensions, and the shock absorbers on other parts of MacPherson strut assemblies can wear out and require replacement, MacPherson strut spring compressor tools have found wide use in the vehicle servicing industry.
One known type of MacPherson strut string compressor is the so-called xe2x80x9cclam shellxe2x80x9d style spring compressor tool. This clam shell type compressor tool generally includes upper and lower arms pivotally attached at one of their ends, with the free ends having clips that engage the coil spring at relative vertical locations. The upper and lower arm pairs each have a trunion located somewhere along their length, and a threaded forcing screw that is threaded into a corresponding threaded hole in the lower trunion and passes through a bore in the upper trunion. A thrust washer assembly has been known to be disposed between the lower surface of the head of the forcing screw and the upper surface of the upper trunion against which it bears to apply compressive force when the forcing screw is tightened.
In prior art McPherson strut spring compressor tools of the clam shell type, it has been known for such a thrust washer assembly to consist of a hard steel washer followed by a softer bronze washer, both located directly below the head of the forcing screw, with the bronze washer abutting against the top of the trunion. It has further been known for the trunion in the region of the forcing screw in some instances to have a square section mounted over the generally cylindrical shape of the trunion, thereby providing a flat upper surface upon which the washer assembly bears. In this way, the generally flat bottom surface of the head of the forcing screw presses generally flat on the flat washers, which press generally flat on the flat top of the square upper trunion section.
The above described clam-shell type MacPherson strut spring compressor tools are in wide use. However, these assemblies suffer from some disadvantages. For example, due to the helical form of the coil spring being compressed, as the forcing screw is tightened to move the arms together, the upper and lower arm sets and their associated trunions do not remain completely parallel. As the trunions are forced out of parallel arrangement by the coil curvature of the spring, a bending load is placed on the forcing screw, and an uneven concentrated load is placed on one region of the washers. Because of the uneven concentrated load distribution, the washers tend to be subjected to a much higher compressive force at one region of the contact with the trunion surface compared to the remaining contact region.
The above-described uneven pressure on the washers can cause the washers to experience wear at the higher force locations. This problem can be exacerbated when a power tool such as an impact wrench is used to actuate the forcing screw. In some instances, the washers may fail eventually due to the wear.
Further, in situations where the washers do fail, if a user continues to use the tool without replacing the damaged washers, the head of the screw will contact the upper trunion surface with a similar degree of uneven pressure, causing the head of the screw to began to cut into the upper trunion, thereby potentially damaging the upper trunion further.
Additionally, the above-described interaction of the forcing screw head, washers, and upper trunion surface, provides a forcing action that tends to resist the tilting of the arms and trunions that naturally would result from the coil shape of the spring. These forces are passed to at least some degree back to the forcing screw itself, such that the forcing screw itself is subjected to bending loads which can undesirably affect the threaded connection between the forcing screw and the lower trunion. These bending loads can make the forcing screw harder to turn and/or can subject the lower threaded connection between the forcing screw and the lower trunion to undesirable wear.
Accordingly, it would be desirable to have a MacPherson strut spring compression tool and method that could overcome, to at least some degree, the wear and/or uneven loading problems described above.
In one aspect, the invention provides an apparatus for compressing a coil spring comprising a hinge assembly. The apparatus further includes a first pair of arms each having one end connected to the hinge assembly and a free end, and a second pair of arms each having one end connected to the hinge assembly and a free end. A first trunion connects the first pair of arms to each other and has a first bore therethrough. Likewise, a second trunion connects the second pair of hinge arms to each other and has a second bore therethrough. A forcing screw having a head portion and a body portion passes through the first bore in the first trunion and threadably engages with the second bore in the second trunion. An adapter having a first surface is disposed to receive force from the head of the forcing screw and has a curved surface that presses against the first trunion.
In another aspect, the invention provides an apparatus for compressing a coil spring comprising a first pair of arms and a second pair of arm. A means for hingedly connecting the first pair of arms to the second pair of arms is also provided. The invention further includes a first connecting means for connecting the first pair of arms to each other and a second means for connecting the second pair of arms to each other. A forcing means passes through a bore in the first trunion and engages the second connecting means. A force transmitting means is disposed to receive the compressive force from the forcing means and transmits the compressive force to the first connecting means. The apparatus also provides a pivoting means for connecting the force transmitting means to pivot relative to the first connecting means.
In still another aspect, the invention provides a method of compressing a respective pair of first arms towards a respective pair of pivotally connected second arms via a first trunion connecting the first arms and a second trunion connecting the second arms. The method includes providing a forcing screw that passes through a bore in the first trunion and threadably engages the second trunion. A pivot adapter is provided between the head of a forcing screw and a surface of the first trunion with a curved surface of the pivot adapter bearing on the first trunion. The forcing screw is rotated to provide a force through the adapter to the first trunion through contact of the curved surface of the adapter with a surface on the first trunion.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.